You can easily set the keg up as a kettle/keggle, MLT and HLT... Just get a good step bit, some drilling lubricant, and take your time drilling it right. For cutting the top, you'll want a good right angle grinder and virgin cutting wheels/disks as well as others to round over the cut edge (so you don't slice yourself open reaching into the keggle).

1/2 barrel kegs are typically the base for this. Allows you to make 5-10 gallon batches (I've managed to fit up to about 14 gallons into the boil keggle so far). As a mash tun, depending on the false bottom setup, and mash thickness, you should be able to get about 30# of grain in there (give or take)... I've already done 30# of grain (plus some rice hulls) in mine. I can get a bit more in there, so I might do 32-33# at some point.

You can easily set the keg up as a kettle/keggle, MLT and HLT... Just get a good step bit, some drilling lubricant, and take your time drilling it right. For cutting the top, you'll want a good right angle grinder and virgin cutting wheels/disks as well as others to round over the cut edge (so you don't slice yourself open reaching into the keggle).

1/2 barrel kegs are typically the base for this. Allows you to make 5-10 gallon batches (I've managed to fit up to about 14 gallons into the boil keggle so far). As a mash tun, depending on the false bottom setup, and mash thickness, you should be able to get about 30# of grain in there (give or take)... I've already done 30# of grain (plus some rice hulls) in mine. I can get a bit more in there, so I might do 32-33# at some point.

It really depends on what you're looking to do and how much you're willing to spend. If you just want to boil in it, you can get away with cutting a hole in the top and then putting in a simple ball valve to drain it out. You do have to get out of the kitchen and put the keg on an outdoor cooker.

That depends... If you're just making a boil keggle, all you need is the ball valve and dip tube inside. Which can be made from one of these dip tubes, and 1/2" ball valves (I prefer the 3 piece for several reasons). Get a few washers,and silicone gaskets or o-rings too. So, in the $45-$50 range for parts for the ball valve assembly. You can add other things as you wish, like a sight tube. I wouldn't bother with a thermometer installed into one, since you can use a fast read, digital, thermometer easily (and use it in more things).

I have my boil keggle equipped with a ball valve assembly (different hardware setup) with TC (TriClove) fittings, a recirculation fitting (above the ball valve setup) for running the boiling wort back into the keggle while sending it through my plate chiller to sanitize, then during the chill phase to do a better job. I also have the sight tube/glass assembly (my own design/make) on mine.

You can go the welded route if you want. I would only do that if you're good with welding (TIG or silver solder) or have a friend that will do it for you. Welders typically charge a good amount for their service.